The present invention is a specific and sensitive method of detecting antibodies in test sera. The method, competitive enzyme-linked immunosorbent assay (ELISA), was developed, in particular, for the detection of human T-cell leukemia-lymphoma virus type III (HTLV-III), the putative causative agent of acquired immune deficiency syndrome (AIDS). This method, however, is generally applicable to the HTLV family of viruses, as well as other antigens and their corresponding antibodies.
Many immunoassay techniques exist for the immunosurveilance of antigens and antibodies. The indirect ELISA assay and the "Western" electroblotting assays are among the most sensitive. However, one of the drawbacks of these procedures is the background interference caused by nonimmune immunoglobulin and other serum factors present in all normal sera. This background, by its tendency to overlap and obscure low levels of specific reactive immunoglobulin, decreases the sensitivity of the assay and creates the need for supplementary confirmation tests in order to demonstrate true positivity. One such confirming test used extensively is the "Western" blotting procedure which, although sensitive, more specific, and informative for distinct viral proteins, is highly labor intensive, difficult to interpret, and is qualitative in nature (rather than quantitative).
The competitive ELISA immunoassay of the present invention greatly increases the sensitivity, specificity, and convenience of obtaining serologic data. The method increases sensitivity of specific antibody measurements by decreasing the background of normal immunoglobulin. The method increases specificity by the use of heterologous antiserum prepared against a virus, thus competitively blocking human specific antibodies.
The present invention is particularly suited to the detection of HTLV-III antibodies. Since AIDS and HTLV-III are known to be transmitted by blood products, a method for detecting contamination with HTLV-III is needed to guarantee the safety of recipients. Such a method should be as sensitive and specific as possible and also easily performed in a routine environment. Tests for viral markers such as reverse transcriptase, viral antigens, or nucleic acid sequences in fresh or cultured blood cells are slow and presently not suitable for large-scale screening. On the other hand, serological tests for viral antibodies or antigens are well suited for this purpsoe, since HTLV-III infected individuals are usually seropositive for antibodies to one or more HTLV-III proteins.